Block sliding down frictionless ramp while being pulled with constant force?

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Homework Help Overview

The problem involves a block of ice sliding down a frictionless ramp at an angle of 60 degrees while being pulled by a constant force. The discussion centers around calculating the work done by various forces acting on the block and understanding the relationship between work and kinetic energy.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning, Problem interpretation

Approaches and Questions Raised

  • Participants discuss the need for formulas related to work and free body diagrams. There are attempts to clarify the meaning of terms like displacement and the implications of constant force on acceleration and kinetic energy. Questions arise about the necessity of knowing the mass of the block and how to approach the calculations for work done by different forces.

Discussion Status

The discussion is ongoing, with participants exploring different interpretations of the problem and questioning assumptions. Some guidance has been offered regarding the use of free body diagrams and the relationship between work and kinetic energy, but there is no explicit consensus on the approach to take.

Contextual Notes

Participants express confusion over the formulas and concepts involved, particularly regarding the role of mass and the implications of constant force on the block's motion. There is an acknowledgment that multiple forces are at play, and the net work done relates to the change in kinetic energy.

soliel021
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Homework Statement


A block of ice slides down a frictionless ramp at theta = 60 degrees while an ice worker pulls on the block (via a rope) with a constant force of 50.0 N. The block slides a distance d = 0.8m along the ramp and its kinetic energy increases by 128 J.
(a) Calculate the work done on the block by the gravitational force.
(b) Calculate the work done on the block by the normal force.
(c) Calculate the percent increase in its kinetic energy if it slid down the ramp the same distance with no rope attached.


Homework Equations


I have no idea, that's my problem!


The Attempt at a Solution


I don't even know where to start!
 
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Do you know the formulas for work and concept of free body diagram(FBD, in short) ?
 
Last edited:
no and yes...

I understand the concept of free body diagrams, but there are so many formulas that I really need help choosing which ones to use for this specific problem.
 
OK. Draw a free body diagram.
For I and II : W = F.r
You know F from FBD for both cases and r is given to you. Use your "intelligence" to find the angle between F and r and calculate the dot product in each case.
 
Last edited:
This may be a really stupid question, but what does "r" stand for? Is it displacement?
 
r really should be s or distance i think...
 
If it has a constant force then that must mean that F=ma is constant, therefore its acceleration isn't changing, as this would alter the force, so how is the block of ice gaining Ek due to a change in velocity?
 
yeah, I don't get it either! and don't I need to know the mass of the block of ice?? I'm so confused...
 
jesus1987 said:
If it has a constant force then that must mean that F=ma is constant, therefore its acceleration isn't changing, as this would alter the force, so how is the block of ice gaining Ek due to a change in velocity?

If there is an acceleration, then velocity is changing.
 
  • #10
soliel021 said:
yeah, I don't get it either! and don't I need to know the mass of the block of ice?? I'm so confused...

you don't need the mass.

Net work done by all forces = change in kinetic energy.

There are 3 forces to consider here. Gravity, the normal force, and the 50N force.

What is the work done by the normal force?

What is the work done by the 50N force?

[tex]W_{gravity} + W_{normal} + W_{50} = 128[/tex]

you can solve for Wgravity using this equation. so the idea is to solve part b) before part a).
 

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